Safety device for motion-picture projectors



y 1949- J. G. SHEPLER 2,471,786 I SAFETY DEVICE FOR MOTION-PICTURE PROJECTORS Filed March 19, 1948 INVENTOR.

JAMES G.SH EPLER 37 ATTORNEY Patented May 31, 1949 SAFETY DEVICE FOR MOTION-PICTURE PBOJECTORS James G. Shepler, Columbus, Ohio Application March 19, 1948, Serial No. 15,814

4 Claims.

This invention relates generally to motion picture projection apparatus and more particularly to a safety device for use in such apparatus to lessen or eliminate the hazard of fire now common in such apparatus. In motion picture projecting machines use is made of a carbon arc lamp which produces a light of great intensity and one which generates intense heat. When the picture machine is in operation, the film is moved past the film gate where light from the arc lamp passes through the film. As long as this film is not exposed an undue length of time in the path of the light from the arc lamp, there is little danger of fire. If, however, the film breaks and jams up in the projecting machine, it may be exposed to the light and heat therefrom for an undue length of time which may cause the film to explode and burn, generating toxic gases and creating a great hazard for the machine operator as well as the patrons of the theater.

One of the objects of this invention is to provide a safety mechanism which will lessen or eliminate the fire hazard by extinguishing the are lamp the instant the film breaks, so that the source of heat will be eliminated.

It is also an object of the invention to provide a safety mechanism including a film controlled switch which will operate to break the circuit for the arc lamp in the event a break in the film occurs, the switch being of such type that it will not create a fire hazard in itself by arcing or otherwise creating a source of heat.

Another object of the invention is to provide a safety mechanism for motion picture projecting machines which mechanism includes a heavy duty relay switch and a low voltage pilot relay circuit including a second relay switch, the first relay switch controlling a circuit of relatively high amperage for operating the arc lamp of the projecting machine, the pilot circuit carrying relatively low voltage so that the potential source of arcing and heat will be very slight.

It is also an object of the invention to include the circuit for the motor Which operates the proj ecting machine in the safety mechanism so that in the event of film breakage the motor will cease to operate, thus decreasing the amount of film which can jam in the machine after the breakage occurs.

It is also an object of the invention to provide a safety mechanism for motion picture projecting machines, which safety mechanism includes a circuit having a film controlled switch, a plurality of relays and current conductors so connected thatwhen the circuits are broken due to breakage or slack in the film, a push button arranged in the circuit will have to be actuated by the operator before the machine can again be put into operation even though the film operated switch may previously be closed.

Another object of the invention is to provide visual indicators in the form of lamps in the circuit to advise the operator of the condition of the circuit.

With these and other objects in view which will appear as the description proceeds the invention consists in the novel features of construction and arrangement of parts more particularly pointed out in the following description of one form of the invention illustrated in detail in the accompanying drawing.

In the drawing:

Fig. 1 is a side elevational view of a motion picture projection machine illustrating somewhat diagrammatically the safety mechanism forming the subject matter of the present invention.

Fig. 2 is a similar View showing the safety mechanism in a different stage of operation.

Fig. 3 is a diagrammatic view illustrating the electric circuits employed in the safety mechanism.

Referring more particularly to the drawing, the numeral 20 designates generally a, motion picture projector. This projector includes a frame 2% having film magazine 22 at the top for film to be displayed and a take-up magazine 23 at the bottom for receiving film which has already been displayed. Between these magazines the frame is provided with the projecting mechanism per so, which mechanism includes a projection lens 2d, a lamp 25 and mechanism 26 between the lamp and the lens for moving the film therebetween intermittently. This mechanism is Well known in the art of motion picture projecting and forms no part of the present invention.

When the motion picture projecting machine 20 is set up for operation, the film from the upper magazine is trained around various sprockets forming a part of the projecting mechanism, per se, and through the mechanism for intermittently moving the film, then it is trained around other sprockets and finally introduced into the take-up magazine 23 where it is wound upon a take-up reel.

At a point adjacent the inlet to the take-up magazine, the frame 2| is provided with a shaft 21 on which is mounted for rocking movement a bell crank member 28. One arm of this member 28 is provided with a pivot 30 on which a small roller 3! is J'ournalled. In the operation 3 of the device the film is passed under the roller 3| so that the roller rides thereon. The other arm of the bell crank 28 is provided with a bracket 32 to hold the glass bulb 33 of a mercury switch 34. Under normal conditions when there is no film in the machine the weight of the mercury switch will cause the bell crank 28 to rock around the shaft '21 to a positionwherein"the mercury in the bulb 33 -do'es not engage both of the contacts 35 and 36 of the switch. The circuit controlled by the switch will then be broken. When theroller 3| is disposed in engagement?- with film= which is properly threaded through the machine," the mercury switch will be held in a position wherein the mercury engages bothcontacts35 and 36 to complete the circuit. V

It should be obvious that if the film should break or slack otherwise develop therein,-thatthe bell crank 28 will rock to a position in which the ':m'e'rcur-y.' switch will break the circuit.-

is connected irfa pilot controlrcircuit for-a sec ond circuit containing:: the motor 37 employed 42 which =-is open when the machine" is not in operation; One side ofthe sw it'chi 32 is con necte'd bya wire43 to one'of 'the'carbon elements 66 of the are light 36, the other carbon 55"being connected by a wire 46 withon'e of a pair contacts and 552 o'fa'heavy dutyrelayfswitch 5n from thecontacts'filandml At th'i'stim'e the are light will' 'be deenergized- Relay. switchtifi's also includes a field-coil 55 for actuating the contactor '54; one end of which coil fis connected with aline 56 'leadingttc'a a commercial sourceof current, generally of 110 volt type, indicated-tin" the "drawingsby the numeral '51,: the 1' other end of the 'coil*SS being'cOnnected:by a line 5B with a contact 66 of a second rel'ay switchtl.

This'relay switch 6| has a complementary contact' 62 which' is directly; connected by: lines 63- and E lwith the source 'of" commercial current 51; Relay'switch- 6| includes -a-contactor 65 which is-normal'ly spaced, when the deviceis 2 inactive; fronrthe contacts-Wand 62; Relay 6| also'ineludes asecond set of contacts fii-and 61, the lat-- ter'of which is connected 'by' aline" 68- withtthe sourceorcurrent 51: by aline 16-w-ith'.one terminal-of the electric motor 31, the other terminal thereof beingconnected by a line H -with' the. current" source 51. Contacts 66 and 67' are connected when the device is-.active,by a 'contactor ll-which also is dis: posed ut of engagement with-thecontacts 66'" and 6'! when the device'isr-inactivel Relay 6| includes a-fieldcoil 13 having one end connected by line with the secondary 150i a low voltage transformer T6, the-primary coil- 710f this-transformer being connected by leads l8 and 86 with the commercial sourceof current 57, The secondary coil 75=ofthe transf0rmer 16-hasaline' 6| extending. therefrom, this lineleading-to con-- tact 35 of the mercury switch 34? Theother contact 36 of this switch is connected-by a line 32 with one of a third set of "contacts 83- and-84-ot the relay 6|. The other of this pair of con- The' relay 'switch 53 i includes: a contactor 5 3 which; w-hen'the device is inoperative; isspaced Contact 66 is connected -sires--oi the operator.

tacts is connected by a line 85 with the second side of field coil 73. This side of coil '13 is also connected with a line 86 which is shunted around the mercury switch 34. Line 86 contains a normally open starting switch 81 by which the operation of the circuit is initiated. A contactor 8B is moved, when coil 73 is energized by the closing of switch 81, into'engagement'withi contacts 83 andr84 to complete and hold the circuit. closed for coil 13. The switch 81 may then be released without danger of the circuit breaking.

Toadvise the-operator that the device is inoperative, a signal light 96 is provided; this light may be suitably located depending upon the de- A second light 3| is pro- Vi-ded to. notify the operator when the device is in operating condition. Lamps 96 and 9| may be of -contrasting colors to render their indications more positive. Lamp QU-is arranged in a circuit including: alead line 62 extending to the current source filandasecond lead line il3- extending tos one of a-pair of contacts Stand forming a part-of-the relay switch 6L. Contactx95-is connected byline-.68- with the-'currentsource 51.

6| isinoperative.

Lamp 9| is connected by a-lead-line Sit-with wire 66 which extends to the-current source 51. It isalso connectedby -aileadtline 97 with one of a pair otcontacts-Qdand lllllwforminglpartof:

relay switchv=53r Contact-Hi6 is: connected with the current source 51 by, lead line 56, When fieldcoil 13 I of relay :6 isideenergized, contactor r 65 will be .spacedifrom contacts B'OMandBZ and field coil 55"of relay sW-itch 53cwillsalso-be de' energized. At this time: a second .contactor. M

of relay. switch 53 'willbe spacedsfrom contacts 98 and M36 i solthat lamps-9| will berdeenergizedl When it is desired to operate-the projection machine, it will be: necessary: innthreadingtthefilm in..the machine; to-positionthel roller 3| on the-filrnas in-d-icated in -Fig; 1 When this rolleris :so positioned, the mercury switch-will be "dise posedto connect wires 8|.and 82= the relay switches 53' and- '6| 1 is -'is ,:necessary: to

operatepush v button switch 87 which twill come plete the pilot circuit for field coil; '73: of relay: When thiscoil-is energized-it will attract -contactor bar- 83- moving the samerinto 1 engagement with contacts. 83 and '84r- As :soon

as this engagement has been-made; thecpush but-- ton may be released sinceztheecircuit for the field-A coil is then completed through contacts-83 and 4 and contactor 83. Also when ileld coil'z-"l3 is er1er-- gized,-contactorT|2-Willbe moved into engagement motor 31. tracts contactori 65 andmoves thesame-intoi engagement with contaets fi El -land 56 2-:complet-ing1the circuit for field coil- 55-of relay; switch 53:

When field. coil 554s energized-sit' will attract contactors B l-andv Hltmoving; thecformer con tactor into engagement-with contacts 7 5| 1 and-i52 and the latter contactor into engagement with The relay-=- switches- '53 and 6 willinoti be operated at this; time however; since contactor88 is spaced from-i contacts 83 and-84, To cause the operationsofcontacts 98 and lllll. At this time lamp 9| will be energized and the circuit for the arc lamp will be in condition for operation at any time the operator desires. It is then necessary for the person operating the machine to merely close the conventional manual switch 42 in the arc lamp circuit to energize this lamp. The act of closing the push button switch is the only act required of the operator in addition to the usual acts required by the conventional machine.

As long as the projection machine operates normally the safety device will be inactive. As soon, however, as a break in the film occurs or slack develops therein from any cause, sufficient to permit the mercury switch 34 to move to the position shown in Fig. 2, the circuit for the field coil '53 will be broken. When this field coil is deenergized, contactors 65 and 12 will move out of engagement with contacts 60 and 62 and 66 and Si, respectively. The current supplied to the machine operating motor 31 will be interrupted and the film feed discontinued. Current supply to the field coil 55 of relay 53 will also be interrupted permitting contactors 54 and lfll to move out of engagement with contacts 5| and 52 and and we, respectively. The circuit for the arc lamp 38 will thus be broken and this lamp extinguished thus discontinuing the source of heat which might ignite the film.

When contacts 93 and loll are disconnected, lamp ill will be extinguished. As previously mentioned, the deenergization of coil 53 permits contactor '12 to engage contacts 94 and 95 to complete the circuit for the lamp 90 which lamp advises the operator that the device is in the projection machine stopping condition.

From the foregoing it will be apparent that a safety device has been provided in which a pilot circuit is employed to control the operation of the conventional circuits for the driving motor and the arc lamp which in some instances have separate current sources. Since the pilot circuit is powered by the same current source as the driving motor any interruption to the source for such motor will cause the discontinuation of current how to the lamp thus preventing the concentration of heat on the film which would other wise occur from the stoppage of the drivin motor. It should also be apparent from the foregoing description that the pilot circuit carries only a low voltage and no danger of fire will be present from this circuit.

While the invention has been shown in one form only it is obvious that many minor changes may be made in the construction and relation of parts without departing from the spirit and scope of the invention as set forth in the following claims.

I claim:

1. Safety mechanism for motion picture projectors of the type having a driving motor and an arc lamp comprising a source of current; a relay switch between said current source and said are lamp; a field coil in said relay switch; a control circuit for said field coil; a second source of current connected in said control circuit, a second relay switch in said control circuit between said second current source and said field coil; a circuit containing said driving motor in parallel with said control circuit; a second field coil in said second relay switch; a pilot circuit containing said second field coil, said pilot circuit being connected with said second current source; a pair of switches connected in series in said pilot circuit one of said switches being controlled by 6 the film and the other being controlled by the field coil in said second relay switch; and a third normally open switch arranged in said pilot circuit in parallel with one of said pair of switches.

2. Safety mechanism for motion picture projectors of the type having a driving motor and an arc lamp comprising a source of current for said are lamp; a relay switch between said current source and said are lamp; a field coil in said relay switch; a second current source; a second relay switch between said second current source and said field coil; a second field coil in said second relay switch; a pilot circuit connected with said second field coil; a first switch in said pilot circuit responsive to the energization of said second field coil; a film controlled switch in said pilot circuit in series with said last-mentioned switch; and a normally open, manually actuated, push button switch shunted around the other two switches in said pilot circuit, the momentary closing or said push button switch when said film controlled switch is closed serving to complete the pilot circuit and to close said first switch to maintain said pilot circuit completed.

3. Safety mechanism for motion picture projectors of the type having a driving motor and an arc lamp comprising a source of current for said are lamp; a relay switch between said current source and said are lamp; a field coil in said relay switch; a second current source; a second relay switch having a field coil and three contactors controlled thereby, one of said contactors governing current fiow from said second current source to the first-mentioned field coil; a circuit for said driving motor, said circuit being controlled by the second contactor of said second relay switch; a manually actuated switch in said driving motor circuit; a transformer having a primary coil connected with said second current source and a secondary coil connected at one end with one end of the field coil of said second relay switch, the third contactor of said second relay switch being connected with the other end of the field coil of said second relay; a film-controlled switch connected with the secondary coil of said transformer and said third contactor; and 2, normally open manually operated switch shunted around said film-controlled switch and said third contactor.

4. In a motion picture projector, a film take-up magazine having a film inlet opening; film guide rolls adjacent said opening; a film guide spaced from said first-mentioned guide rolls; a bell crank member mounted for pivotal movement adjacent said film inlet opening; a roller journalled on one arm of said bell crank member, said roller normally engaging film extending between said spaced guide rolls and guide; a mercury tube switch carried by the other arm of said bell crank, said switch having spaced contacts electrically connected when said roller is engaged with said film; a relay switch having a field coil and three contactors controlled thereby; a pilot circuit for said field coil, said pilot circuit having one of said contactors and said mercury tube switch in series; a normally open, manually actuated switch shunted around said mercury switch and the contactor arranged in said pilot circuit; a driving motor; a circuit for said driving motor, said circuit being controlled by another of the contactors of said relay switch; an arc lamp; a second relay switch for controlling the operation of said are lamp, said second relay switch having a field coil and a contactor; and a circuit for the field coil of said second relay, the latter circuit 

